This invention relates generally to systems for passive removal of subsurface contaminants and flow measurement. More specifically, this invention is a passive removal valve apparatus for removing subsurface contaminants integrated with a volumetric flow meter.
Contaminants can exist in subsurface soil and groundwater in the liquid or vapor phase as discrete substances and mixed with and/or dissolved in groundwater and soil gases. Various contaminants can be found in groundwater and soil, such as volatile compounds, including volatile organic compounds, nonvolatile materials, and metal contaminants. Such contaminants can be found and dealt with in the vadose (unsaturated) zone found between the surface of the earth and the water table, at the interface between the vadose zone and the water table, and in the saturated zone below the water table.
There are many proposed methods for removal of surface contaminants, such as excavation followed by incineration, in situ vitrification, biological treatment, chemical additives for deactivation, radiofrequency-heating, etc. Although successful in some applications, these methods can be very expensive (hundreds of dollars per ton) and are not practical if many tons of soil must be treated.
One example of low cost, efficient contaminant extraction is disclosed in U.S. Pat. No. 5,641,245 to Pemberton et al., which is incorporated herein by reference. The Pemberton patent discloses an apparatus for passively removing subsurface contaminants. The apparatus provides a means for opening and closing a valve (the xe2x80x9cBaroballxe2x80x9d valve) as the atmospheric and subsurface pressures differ from one another. Basically, the apparatus allows a well to breathe out contaminants during low atmospheric pressure.
The apparatus includes a riser pipe extending through a well into the ground reaching a position above the water table, where contaminants are likely to be present. The end of the pipe positioned above the water table contains perforations allowing contaminant vapors to enter the pipe. A portion of the riser pipe extends upward above the ground and is in fluid communication with a valve. The valve is formed to have a low cracking pressure and is responsive to changes in ambient atmospheric pressure.
The Baroball valve is formed from a vertically oriented chamber having a conic shaped valve seat. A ball is disposed in the valve chamber and rests on the valve seat when equalization of atmospheric and subsurface pressure exists. Cracking pressure, the pressure required to lift the ball, is related to the density or weight and surface area of the ball and is preferably no more than about one mbar. As subsurface pressure rises above atmospheric pressure the ball rises in the valve chamber allowing contaminants to escape through the valve out into the atmosphere.
The benefits of the Baroball valve are numerous. The valve provides passive release of contaminants from a well with minimal construction costs, maintenance, and operation costs, and additionally requires no external energy source. The Baroball valve further prevents the flow of air into a well, and thereby increases the amount of contaminants that are released during periods of low pressure by preventing dilution of contaminants in the well. The valve enclosure is also transparent, semi-transparent, or is formed to have a window, so that malfunctioning of the apparatus can be visually detected. Thus, the valve provides a low cost method of removing subsurface contaminants.
However, there are disadvantages associated with the Baroball apparatus. Although the Baroball valve provides passive release of subsurface contaminants, it does not provide a mass flow measurement of the amount of contaminants released through the valve. Therefore, an external device must be used to measure the mass flow through the valve by combining independent measurements of volume flow rate with contaminant concentration. Many external apparatuses, for attachment to the Baroball valve, exist for measuring volume flow through the valve mechanism. Several are discussed below.
U.S. Pat. No. 4,873,873 to Day discloses a system for metering the flow rate of air through a duct in which gates are pivotally mounted and connected together to vary the area of the duct. The gates are balanced so as to be effectively weightless. The forces on and the positions of the gates correspond to the pressure and the flow rate in the duct.
U.S. Pat. No. 5,616,841 to Brookshire is directed to a metering pipe system that is positionable in fluid communication with a well in a landfill for determining gas flow rate through the well. The device includes an upstream segment and a downstream segment coupled together and separated by an orifice plate. Specifically, the segments are advanced into the coupling toward each other, on opposite sides of the orifice plate from each other. Upstream and downstream pressure ports are respectively formed through the walls of the upstream and downstream segments and the coupling adjacent the orifice plates. The difference in pressure at the ports is correlated to a flow rate through the pipe.
U.S. Pat. No. 4,559,834 to Phillips et al. is directed to a flow meter arrangement including an elongated body adapted to be disposed in an upright position with a typical rotameter design utilizing a floating ball mechanism. The flow meter design has a first valve at the base of the rotameter tube and a second valve at the top of the rotameter chamber. The flow meter arrangement can be adapted for pressure or vacuum applications.
U.S. Pat. No. 5,099,698 to Kath et al. is directed to an electronic readout for a rotameter flow gauge which includes a means for optically scanning the rotameter flow gauge and determining the position of a float within the rotameter.
Finally, U.S. Pat. No. 5,379,651 to Doolittle is directed to an improved electronic monitoring arrangement for a rotameter device utilizing a single point source of radiation at one side of the rotameter and a vertical array of detectors diametrically opposite to it. The elevation of the radiation source is identical to the uppermost elevation of the radiation detectors. The elevation of the rotameter float will intersect the vertical array of detectors allowing for a reading of the flow rate.
The above references provide systems and methods of measuring airflow mass. However, each requires that it be attached to the passive contaminant removal system. An external flow meter device placed in fluid communication with the passive valve is disadvantageous for several reasons.
First, the passive valve is just that, passive. The Baroball valve requires no external power source. Thus, multiple valves can be deployed in the field without building an infrastructure for providing power to the removal system. Most flow-meter systems require an external energy source for powering the measuring device. Therefore, all electronic flow meters requiring external energy diminish the advantages gained by a passive system. Although flow meters exist that do not require external energy sources, these devices like their electronic counterparts cause back pressure that hinders the operation of the passive valve.
The Baroball system operates in a very narrow pressure differential range, generally a few mbars. A mbar change in pressure can cause the valve to open, releasing contaminants. Therefore, any back pressure or airflow constriction caused by an external flow meter device can cause the valve to malfunction. Additionally, one advantage of the Baroball system is to provide a low cost and low maintenance contaminant removal option. Thus, external flow meter devices add unnecessary expense; thereby defeating the Baroball system""s low cost advantage.
Consequently, a need exists for a passive removal system for subsurface contaminants including a volume flow meter such that the volume flow meter operates without hindering operation of the valveor adding unnecessary costs.
This invention relates to an improvement on the Baroball valve. In one embodiment, the valve mechanism of the Baroball is modified to serve as a rotameter bob. Additionally, the valve seat and walls are modified to form the measuring chamber. In a second embodiment, deployed Baroball valves are retrofitted to include two ports, one on each side of the valve and in fluid communication with a static pressure device. The flow rate, through the valve, is proportional to the pressure drop across the device.
Among objects of this invention are to:
provide a passive subsurface contaminant removal system that measures the volume flow of contaminants passing through the valve;
provide a method to retrofit an existing Baroball valve so it measures volume flow of the contaminants passing through the valve; and
provide a volume flow-measuring device that does not hinder the operation of the Baroball valve.